The dopamine transporter is a key target or "receptor" for cocaine that mediates its addicting properties. Therefore, understanding the factors which control the levels of dopamine transporter in brain is essential for understanding mechanisms of drug addiction. This project plans to develop a method to measure the synthesis rate and degradation rate of the dopamine transporter, and the serotonin transporter as well. The serotonin transporter is important because it is a target or receptor for antidepressant drugs. Substantial progress has been made in that the serotonin transporter turnover has been measured and its half-life is 3.4 days. We are in the process of determining the same factors for the dopamine transporter.